JP2002016013A - Method for manufacturing silicon carbide semiconductor device - Google Patents

Abstract

(57) [Summary] (Problem corrected) [PROBLEMS] A silicon carbide semiconductor device capable of forming an impurity diffusion layer having a high carrier concentration by being electrically activated and forming a good ohmic contact And a method for producing the same. SOLUTION: A carbon thin film 2 and a tungsten silicide film 3 are stacked on the entire surface of a silicon carbide substrate 1 by using a sputtering deposition method or a chemical vapor deposition method, and after removing the tungsten silicide film 3 in a diffusion region, the carbon thin film 2 is formed. After aluminum ions 4 were implanted from above, 1
The carbon thin film 2 is removed by oxygen plasma at a high temperature of 600 ° C., and the ion beam mixing layer is removed by plasma etching.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a silicon carbide semiconductor device, and more particularly, to a method of manufacturing a silicon carbide semiconductor device that can make good contact on the surface of a semiconductor substrate.

[0002]

2. Description of the Related Art Conventionally, silicon carbide (hereinafter referred to as SiC)
Manufacturing method of forming impurity diffusion layer on surface of semiconductor substrate
Are known (for example, VLSI by SM SZE,
 Technology, McGRAW-HILL out
Edition, P347). In the above prior art, a semiconductor of SiC is used.
Silicon dioxide (hereinafter referred to as SiO) _TwoDescribed as) membrane
And selectively form impurity atoms in the part where the diffusion layer is formed.
After annealing, perform annealing at high temperature.
ing. In this manner, the SiO_TwoForm a film
The surface of the chemically active semiconductor substrate.
Protection and channeling during ion implantation,
In addition, outward diffusion of impurities implanted during annealing
Preventing.

[0003]

SUMMARY OF THE INVENTION As is well known, Si
Since the C substrate has a very small diffusion coefficient of impurity atoms,
When a thick diffusion layer is to be formed, it is necessary to perform ion implantation a plurality of times while changing the projection range of the ion implantation when implanting impurities. In the impurity diffusion layer, for example, an element region such as a source region or a drain region is generally formed by a MOSFET or the like.
The metal for electric wiring is laminated on the element region. In order to realize good electrical connection between the surface of the diffusion layer and the metal for electric wiring, that is, to realize ohmic contact, the contact portion is formed. In the vicinity of the diffusion layer interface, it is desirable to increase the impurity concentration and electrically activate to increase the carrier concentration.

[0004] However, when ion implantation is performed with the projection range adjusted so that impurities are introduced near the interface of the diffusion layer in the state where the SiO ₂ film is formed on the SiC substrate as in the prior art, The impurities to be impinged collide with the SiO ₂ film formed on the SiC substrate and are decomposed, so that a phenomenon called knock-on occurs in which Si atoms and especially oxygen atoms are injected into the SiC substrate, and the crystallinity of the SiC substrate surface is destroyed. Would. In the subsequent heat treatment such as annealing, the crystallinity is somewhat recovered, but the crystallinity is not recovered until the carrier concentration is high due to the electrical activation for realizing the ohmic contact. That is, in the above-described conventional technology, the diffusion layer on the surface of the SiC substrate is not electrically activated for realizing ohmic contact, so that a state in which the carrier concentration is high cannot be obtained. The present invention has been made in view of the above-mentioned problems, and a method of manufacturing a SiC semiconductor device in which a diffusion layer is electrically activated for realizing ohmic contact on a surface of a SiC substrate to obtain a high carrier concentration state. The purpose is to provide.

[0005]

According to a first aspect of the present invention, there is provided a method of manufacturing a silicon carbide semiconductor device, comprising: forming a thin film containing carbon on a silicon carbide semiconductor substrate; From the step of ion-implanting impurities exhibiting electrical activity from the silicon carbide semiconductor substrate until reaching the silicon carbide semiconductor substrate, and heating the silicon carbide semiconductor substrate at a temperature lower than the temperature at which the thin film starts to decompose or evaporate,
Removing the thin film. According to a second aspect, in the method of manufacturing a silicon carbide semiconductor device according to the first aspect, the thin film is made of boron carbide or aluminum carbide, and the impurity uses at least one of aluminum and boron. In claim 3,
2. The method for manufacturing a silicon carbide semiconductor device according to claim 1, wherein said thin film is carbon nitride, and said impurity uses at least one of phosphorus, nitrogen, arsenic and ammothin.

According to a fourth aspect of the present invention, in the method of manufacturing a silicon carbide semiconductor device according to the first aspect, the heating step includes mixing oxygen and silicon in the atmosphere to eliminate the thin film, and then forming silicon and silicon dioxide. The surface mixing layer is oxidized at a temperature at which the surface mixing does not evaporate, and the surface mixing layer is removed using a chemical solution containing hydrofluoric oxygen. According to claim 5, a step of forming an aluminum carbide thin film on a silicon carbide semiconductor substrate, a step of ion-implanting impurities exhibiting electrical activity from the thin film until reaching the silicon carbide semiconductor substrate, Heating the semiconductor substrate at a temperature lower than the temperature at which the thin film starts to decompose or evaporate, immersing the silicon carbide semiconductor substrate in pure water to decompose and remove, and at a temperature at which silicon and silicon dioxide do not evaporate. The method includes a step of oxidizing the surface mixing layer, a step of removing the surface mixing layer using a chemical solution containing hydrofluoric oxygen, and a step of removing the thin film.

[0007]

According to the present invention, a thin film containing carbon is formed on a silicon carbide semiconductor substrate, and impurities having electrical activity are ion-implanted from the thin film until reaching the silicon carbide semiconductor substrate. Is heated at a temperature lower than the temperature at which the thin film starts to decompose or evaporate, so that the thin film is removed, so that oxygen atoms that would destroy crystallinity are not injected into the silicon semiconductor substrate, Therefore,
Since the impurity diffusion layer having a high carrier concentration can be formed by being electrically activated, a favorable ohmic contact can be realized.

[0008]

FIG. 1 is a block diagram showing an embodiment of the present invention.
This will be described with reference to FIGS. A method of manufacturing a semiconductor device according to the present embodiment will be described. As shown in FIG. 1, 100 n is formed on the entire surface of a SiC semiconductor substrate (hereinafter referred to as SiC substrate) 1.
The carbon (graphite) thin film 2 having a thickness of m is laminated by a sputtering deposition method using a carbon target or a chemical vapor deposition (CVD) method of reducing a hydrocarbon-based gas such as methane or butane.

Next, a tungsten silicide film having a thickness of 800 nm is laminated on the entire surface of the carbon thin film 2 by a CVD method, and then the portion of the tungsten silicide film where a diffusion layer is to be formed is removed by photolithography and etching, as shown in FIG. Such a mask 3 is formed. Si
In C, S was added to recover the crystallinity after ion implantation.
Since the ion implantation is performed while the temperature of the iC substrate is raised to a high temperature of 500 ° C. or more, it is necessary to use a tungsten silicide film or the like that can withstand this high temperature instead of a photoresist generally used for a silicon substrate. is there.

Next, aluminum ions 4 are supplied at 200 KeV.
(FIG. 2). By this ion implantation,
In a region where the mask 3 is not formed (a diffusion layer is formed), carbon atoms C and aluminum ions Al are generated on the surface of the SiC substrate 1 by collision between the ion-implanted aluminum ions 4 and the carbon thin film 2. Is done. FIG. 3 shows a profile obtained by determining the presence of each atom and ion in the depth direction.

The numerical value in the depth direction in FIG.
The range up to 100 nm indicates the carbon thin film 2 and is 100 nm.
The range up to 500 nm indicates the SiC substrate 1.
That is, the contact surface between the carbon thin film 2 and the SiC substrate 1 is 100
nm in depth. In FIG. 3, the solid line shows the relationship between the depth and the concentration of the ion-implanted aluminum ions Al, and the broken line shows the relationship between the depth of the carbon atoms C and the concentration. Aluminum ions Al are distributed over a depth of 100 nm to 350 nm (region a). Carbon atom C is 250
It is distributed at a concentration of 1 × 10 ¹⁸ atoms / cm ³ up to nm (region b). In the present embodiment, since an SiO ₂ film is not used unlike the related art,
Naturally, oxygen is not knocked on the surface of the SiC substrate 1. Therefore, the destruction of crystallinity due to this oxygen does not occur. The concentration of carbon atoms C in the extremely surface layer x of the SiC substrate 1 from 100 to 110 nm is 1 × 10 ²² atoms.
This is a region where the concentration becomes extremely high as s / cm ^3, and the material existing near the interface is uniformly mixed by an operation called ion beam mixing, and cannot be used as a SiC semiconductor material. I do.

Next, after ion implantation, the mask 3 is removed, and high-temperature annealing at 1600 ° C. using an induction heating method is performed. At this time, although the single crystal structure is broken in the ion-implanted region of the SiC substrate 1 including the region where the carbon atoms C are generated, the SiC semiconductor substrate 1 is annealed by annealing.
The impurities are activated while the crystal gradually recovers from the non-destructive region interface on the back side of the ion beam mixing layer x.
The recovery stops when it reaches the border with. In the activation of the impurities, the amount of generated carriers is improved about 10 times in the region b into which the carbon atoms C have been implanted, and a high carrier concentration can be obtained with a small amount of implanted ions.

Next, the carbon thin film 2 is removed from the SiC substrate 1 by oxygen plasma. Next, the ion beam mixing layer (region x) is removed by plasma etching using a mixed gas of CF ₄ and oxygen, a mixed gas of chlorine gas and oxygen gas, or another gas having an etching property. Alternatively, after oxidizing the ion beam mixing layer x at a temperature of about 1200 ° C. or lower, the ion beam mixing layer x is removed with a chemical solution containing oxygenated water.

As described above, in the present embodiment, S
Since a carbon thin film 2 is laminated on an iC substrate 1, a mask 3 is formed thereon, and aluminum ions 4 are implanted.
Since the impurity diffusion layer is not injected into the C substrate 1 and is thus electrically activated to form an impurity diffusion layer having a high carrier concentration, a good ohmic contact can be realized. In the case of using the SiO ₂ film in the conventional SiC substrate 1 surface and thus roughened SiC substrate 1 surface and then re-react with the SiC substrate 1 at the interface or evaporates SiO ₂ film by annealing, in this embodiment In order to protect the surface of the SiC substrate 1 by using the carbon thin film 2 to withstand high-temperature annealing,
No surface roughness occurs.

In the above annealing, the atmosphere containing oxygen is used as the carbon thin film 2 formed by the reaction between carbon and oxygen.
By matching the total of the disappearance amount of the SiC substrate 1 and the oxidation amount of the ion beam mixing layer x on the surface of the SiC substrate 1 with the annealing time, the annealed surface of the SiC substrate 1 has a thin SiO ₂ film 5 as shown in FIG. Can be formed, and the SiO ₂ film 5 can be easily removed with a hydrofluoric acid-based etchant, so that the steps of ion implantation and activation can be further simplified.

In the SiC substrate 1, a substrate having an SiC epitaxial layer 6 formed on the SiC substrate 1 may be used in order to reduce defects. Although the formation of the epitaxial layer 6 is very expensive, according to the present embodiment, the ion beam mixing layer x removed on the surface of the SiC substrate 1 is as thin as 10 nm. There is no waste.

In the ion implantation, the number of ions is quantified by counting the electric charge transferred when the ionized element is accelerated by an electric field and collides with the target sample. However, when the target sample surface is an insulating film, In this case, the charge is charged up on the target sample surface, and when this charge-up becomes a high voltage, the quantity of incident ions is shifted, the ion trajectory is bent, and the implantation energy is shifted. The implanted ions become non-uniform in the substrate surface. Therefore, a technique called an electroshower in which an amount of electrons matched to the amount of injection is applied to the surface of the target sample is applied. However, it is necessary to adjust the irradiation amount according to the amount of ion implantation. On the other hand, in the present embodiment, since the carbon thin film 2 is conductive and charge-up itself does not occur in the first place, there is no problem of abnormal injection on the surface of the target sample.

In the above-described embodiment, a graphite film is used as the carbon thin film 2. However, when carbon is used as the thin film 2, impurities such as boron, aluminum, phosphorus, and arsenic may be used as implanted ions. Has the same effect. When the thickness of the carbon thin film 2 is increased, the profile of the ion-implanted atoms becomes gentler, and the energy is changed in multiple steps called box implantation peculiar to the SiC substrate 1 to reduce the number of steps of the ion implantation process. And it is possible to secure a knock-on atomic weight.

In this embodiment, the carbon thin film 2 is laminated on the surface of the SiC substrate 1. However, as shown in FIGS. 5 and 6, aluminum carbide Al ₄ C ₃ (mp 2200 ° C.) or boron carbide B ₄ When the carbon compound 7 such as C (mp 2350 ° C.) is used, the same effect as in the above-described embodiment is obtained, and at the time of high-temperature annealing, the dissolution temperature of the carbon compound 7 on the surface is about 2200 ° C., and sublimation in vacuum is started. Since the temperature is 1800 ° C., it sufficiently functions as a protective film up to 1700 ° C., so that occurrence of roughness on the SiC surface can be prevented. Further, aluminum carbide is decomposed into aluminum hydroxide and methane only by being clarified with water after subsequent annealing, and the aluminum carbide can be removed, thereby reducing the number of steps. When phosphorus or arsenic is used as the ions to be implanted, the same effect can be obtained by laminating carbon nitride 8 on the surface of SiC substrate 1 as shown in FIG.

[Brief description of the drawings]

FIG. 1 is a view showing a step of laminating a carbon thin film on a silicon carbide substrate of an embodiment.

FIG. 2 is a view showing a step of implanting aluminum ions.

FIG. 3 is a profile showing the relationship between the depth and concentration of aluminum ions and carbon atoms.

FIG. 4 is a view showing a surface of a silicon carbide substrate after annealing.

FIG. 5 is a view showing a step of laminating a carbon compound on a silicon carbide substrate.

FIG. 6 is a profile showing the relationship between the depth and concentration of aluminum ions and carbon compounds.

FIG. 7 is a view showing a step of stacking carbon nitride on a silicon carbide substrate.

[Explanation of symbols]

REFERENCE SIGNS LIST 1 SiC semiconductor substrate 2 carbon thin film 3 mask 4 aluminum ion 5 SiO ₂ film 6 SiC epitaxial layer 7 carbon compound 8 carbon nitride

Claims (5)

[Claims] A step of forming a carbon-containing thin film on a silicon carbide semiconductor substrate; a step of ion-implanting an electrically active impurity from the thin film until reaching the silicon carbide semiconductor substrate; A method for manufacturing a silicon carbide semiconductor device, comprising: a step of heating a semiconductor substrate at a temperature lower than a temperature at which the thin film starts to decompose or evaporate; and a step of removing the thin film. 2. The method of manufacturing a silicon carbide semiconductor device according to claim 1, wherein said thin film is boron carbide or aluminum carbide, and said impurity uses at least one of aluminum and boron. Manufacturing method. 3. The method for manufacturing a silicon carbide semiconductor device according to claim 1, wherein said thin film is carbon nitride, and said impurity uses at least one of phosphorus, nitrogen, arsenic, and ammotin. A method for manufacturing a semiconductor device. 4. The method for manufacturing a silicon carbide semiconductor device according to claim 1, wherein said heating step comprises mixing oxygen in an atmosphere to eliminate said thin film, and thereafter, a temperature at which silicon and silicon dioxide do not evaporate. And oxidizing the surface mixing layer by using a chemical solution containing hydrofluoric oxygen to remove the surface mixing layer. 5. A step of forming an aluminum carbide thin film on a silicon carbide semiconductor substrate, a step of ion-implanting impurities exhibiting electrical activity from the thin film until reaching the silicon carbide semiconductor substrate, and A step of heating the substrate at a temperature lower than a temperature at which the thin film starts to decompose or evaporate; a step of immersing the silicon carbide semiconductor substrate in pure water to decompose and remove the surface; Manufacturing a silicon carbide semiconductor device, comprising: a step of oxidizing a mixing layer; a step of removing the surface mixing layer using a chemical solution containing aqueous hydrogen fluoride; and a step of removing the thin film. Method.